1. Field of the Invention
The present invention relates generally to the separation of gaseous or vapor phase species by means of immobilized liquid membrane (ILM) materials. More particularly, the invention concerns the removal of water vapor from the ambient atmosphere of a conditioned space.
2. Background Art
Numerous approaches to the separation of one gas from a mixture of gases by preferential differential permeation have been investigated over the years. Membrane systems for the separation of gases are potentially attractive because they offer low capital and operating costs, along with low energy consumption requirements. Stabilized immobilized liquid membranes (ILM's) which achieve the simultaneously high permeability and selectivity associated with earlier ILM's together with an extremely high flux in a manner which overcomes the time variable stability problems associated with early ILM's are described in U.S. Pat. No. 4,710,205 assigned to the same assignee as the present invention. That application also describes in detail how the Kelvin effect operates to increase the stability of immobilized liquid membranes with reference to the lowered vapor pressure of the liquid contained in the membrane pores. To the extent that material from that application is required to supply any additional information relevant to the understanding of material in this application, it is hereby incorporated by reference.
The detrimental effect of high relative humidity with respect to the environment of a controlled space, is well known both as to its effects regarding the comfort of the occupants and with respect to items which need to be stored at lower relative humidity to prevent damage from phenomena associated with prolonged high humidity exposure. For these and many other reasons, humidity control has become a necessity for a wide variety of types of conditioned spaces.
Prior to the utilization of membrane-type separation techniques, the most widely practiced method of removing water vapor from a conditioned space involved condensing moisture contained in the atmosphere by cooling the atmosphere below the dew point. This method works very well with respect to the reduction of high humidities to reasonable humidity readings, however, it does require large quantities of energy to be expended to achieve condensation of the moisture.
Other methods include the use of hygroscopic agents or salts to remove moisture from the atmosphere. This technique has been most often associated with the removal of additional water vapor at lower humidities to achieve a relatively dry state. The salts, of course, must also be regenerated or discarded after absorbing quantities of water.
Still there remains a need, however, for a practical, stable, continuously operable system for the removal of condensable gas, especially water vapor, which combines long life with low energy consumption.